Double-strand breaks in DNA caused by repair of damage due to ultraviolet light

DNA DSBs are formed in normal human IMR-90 cells during repair incubation after 100 and 300 J.m-2 of UVL. By contrast, no DSBs are formed after UVL in human XPA cells that are unable to excise pyrimidine dimers. The DSBs are not due to immediate cell death since all the cells excluded trypan blue at the time of assay and because XPA cells, which are much more UVL-sensitive than IMR-90, did not form DSBs after UVL. We suggest that these repair-induced DSBs should be potent lesions that might lead to cytotoxicity, chromosome aberrations, deletion mutations, and perhaps cellular transformation. transformation.